Yuexiang Huang

Enhanced visible light photocatalytic activity of Gd-doped BiFeO3 nanoparticles and mechanism insight.

To investigate the effect of Gd doping on photocatalytic activity of BiFeO3 (BFO), Gd-doped BFO nanoparticles containing different Gd doping contents (Bi(1−x)GdxFeO3, x = 0.00, 0.01, 0.03, 0.05) were synthesized using a facile sol-gel route. The obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, and ultraviolet-visible diffuse reflectance spectroscopy, and their photocatalytic activities were evaluated by photocatalytic decomposition of Rhodamine B in aqueous solution under visible light irradiation. It was found that the Gd doping content could significantly affect the photocatalytic activity of as-prepared Gd-doped BFO, and the photocatalytic activity increased with increasing the Gd doping content up to the optimal value and then decreased with further enhancing Gd doping content. To elucidate the enhanced photocatalytic mechanism of Gd-doped BFO, the trapping experiments, photoluminescence, photocurrent and electrochemical impedance measurements were performed. On the basis of these experimental results, the enhanced photocatalytic activities of Gd-doped BFO could be ascribed to the increased optical absorption, the efficient separation and migration of photogenerated charge carriers as well as the decreased recombination probability of electron-hole pairs derived from the Gd doping effect. Meanwhile, the possible photocatalytic mechanism of Gd-doped BFO was critically discussed.

Facile Synthesis of Highly Efficient p–n Heterojunction CuO/BiFeO3 Composite Photocatalysts with Enhanced Visible‐Light Photocatalytic Activity

A novel heterostructured CuO/BiFeO3 composite photocatalyst was successfully prepared through a simple combination of hydrothermal and impregnation process. CuO was uniformly deposited on the surface of BiFeO3 particles with a p–n heterojunction formed at the interface between CuO and BiFeO3. CuO/BiFeO3 heterostructured photocatalysts improved the UV/Vis spectral absorption ability, and exhibited enhanced photocatalytic activities for photodegradation of methylorange or a colorless compound (i.e., phenol) under visible light. In addition, after five recycles for the photodegradation of methylorange, CuO/BiFeO3 did not exhibit significant loss of photocatalytic activity, confirming its stability and long‐time reusability. The enhanced photocatalytic activity could be mainly ascribed to the p–n heterojunction structure between CuO and BiFeO3, which could significantly facilitate the separation and transfer of photogenerated electron–hole pairs. On the basis of the calculated energy bands, the photocatalytic mechanism was also proposed.

Pd cocatalyst on Sm-doped BiFeO3 nanoparticles: synergetic effect of a Pd cocatalyst and samarium doping on photocatalysis

To explore the synergetic effect of rare earth doping and noble metal cocatalyst loading on the photocatalytic activity of BiFeO3 (BFO), in this work, novel Pd cocatalyst-loaded and Sm-doped BFO (Pd/BSFO) composite photocatalysts containing different Pd loading contents were successfully prepared by using a sol–gel method followed by an impregnation process. The experimental results revealed that the rhombohedral structure of BFO was distorted by Sm substitution, and Pd cocatalyst nanoparticles were uniformly deposited on the surface of BSFO particles with the formation of a heterojunction at the interface between Pd and BSFO. Compared to the BFO, BSFO and Pd/BFO sample, the Pd/BSFO samples exhibited improved UV-vis spectral absorption ability and significantly enhanced photocatalytic activities for the photodegradation of methyl orange or a colorless compound (i.e., phenol) under visible light irradiation. When the Pd loading amount on the surface of BSFO was 1.5 wt%, the optimal photocatalytic degradation efficiency was achieved. The enhanced photocatalytic activity of the Pd/BSFO photocatalyst could be attributed to the increased optical absorption, the efficient charge transfer and separation as well as the suppressed recombination of photogenerated electron–hole pairs derived from the Sm dopant trapping level and the heterojunction formation of the Schottky barrier between BSFO and the Pd cocatalyst in Pd/BSFO, as verified by photoluminescence (PL) emission spectra, photocurrent action spectra and electrochemical impedance spectra (EIS). On the basis of the calculated energy bands and trapping experiments, the photocatalytic mechanism was also discussed.

Controllable synthesis of well-ordered TiO 2 nanotubes in a mixed organic electrolyte for high-efficiency photocatalysis

Well-ordered TiO2 nanotube arrays (TNAs) were fabricated by electrochemical anodization in a mixed organic electrolyte consisting of ethylene glycol and glycerol. The morphology, structure, crystalline phase, and photocatalytic properties of TNAs were characterized by using TEM, SEM, XRD and photodegradation of methylene blue. It was found that the morphology and structure of TNAs could be significantly influenced by the anodization time and applied voltage. The obtained tube length was found to be proportional to anodization time, and the calculated growth rate of nanotubes was 0.6 μm/h. The microstructure analysis demonstrated that the diameter and thickness of the nanotubes increased with the increase of anodization voltage. The growth mechanism of TNAs was also proposed according to the observed relationship between current density and time during anodization. As expected, the obtained TNAs showed a higher photocatalytic activity than the commercial TiO2 P25 nanoparticles.

Oxygen vacancies induced by zirconium doping in bismuth ferrite nanoparticles for enhanced photocatalytic performance

Doping with certain foreign metal ions in a photocatalyst might introduce surface defects (such as extrinsic oxygen vacancies), which can probably play an important role in the photocatalytic performance. In this work, oxygen vacancies were for the first time introduced into bismuth ferrite (BiFeO3, denoted as BFO) nanoparticles by zirconium (Zr) doping, and the relationship between oxygen vacancies and the photocatalytic activity of Zr-doped BFO was investigated. It was found that the optical properties and the photocatalytic activities of Zr-doped BFO photocatalysts were significantly affected by the Zr doping amount. The Zr-doped BFO photocatalysts showed much higher photocatalytic activities for methyl orange degradation or Cr(VI) reduction than the pristine BFO. When the Zr doping content was 2mol%, the highest photocatalytic efficiency was achieved, which was more than two times that of the pristine BFO. The boosted photocatalytic performance of Zr-doped BFO was mainly attributed to the presence of surface oxygen vacancies induced by Zr doping, which could act as electron traps and active sites to promote the efficient separation and migration of photogenerated charge carriers, as verified by the trapping experiments and the photoelectrochemical measurements. Thus, the present work provides a simple approach to introduce oxygen vacancies in semiconductor photocatalysts through metal ion doping with a great potential for development of efficient visible light photocatalysts, and also enlarges the understanding of surface-defect dependence of photocatalytic performance for environmental remediation.

The Development of Novel Electrolyte Membrane with High Proton Conductivity at Medium Temperatures

A novel electrolyte membrane PVDF-Al2O3-CsHSO4 usable at medium temperatures was prepared by composite of PVDF and an inorganic proton conductor Al2O3-CsHSO4. The membrane has a steep increase in proton conductivity around 90°C and retains the high conductivity, about 10-3 S•cm-1, up to 200°C. The incorporation of Al2O3-CsHSO4 with PVDF leads to a dramatic improvement of the properties of PVDF, including widen the phase transition temperature of CsHSO4, improve proton conductivity and enhance chemical stability over wide temperature range.

Hydrogen Generation by Hydrolysis of the Ball Milled Al-C-KCl Composite Powder in Distilled Water

In the present investigation, the Al-C-KCl composite powders were prepared by a ball milling processing in an attempt to improve the hydrogen evolution capacity of aluminum in water. The results showed that the hydrogen generation reaction is affected by KCl amount, preparation processing, initial aluminum particle size and reaction temperature. Increasing KCl amount led to an increased hydrogen generation volume. The use of aluminum powder with a fine particle size could promote the aluminum hydrolysis reaction and get an increased hydrogen generation rate. The reaction temperature played an important role in hydrogen generation rate and the maximum hydrogen generation rate of 44.8 cm3 min-1g-1of Al was obtained at 75oC. The XRD results identified that the hydrolysis byproducts are bayerite (Al(OH)3) and boehmite (AlOOH).

Preparation of Well-Ordered TiO2 Nanotube Arrays by Electrochemical Anodization of Titanium Foil in Neutral Electrolytes

To obtain high performance TiO2 nanotube arrays (TNAs)-based material is interesting because of its wide applications in photocatalysis field such as solar energy conversion, photocatalysis and sensors. In the present work, the well-ordered TNAs were prepared by electrochemical anodization of titanium foil in the SO42−/F− based electrolyte under 20 V for 2 h during which the Ti foil and Pt wire were used as anode and cathode, respectively. The FESEM results showed that the as-obtained TNAs were well-aligned on Ti substrate with ~ 1.5 μm in length and ~ 100 nm pore in diameter. The XRD results indicated that the as-formed TNAs was in the form of amorphous and could be transformed into crystalline anatase phase under the heat treatment at 450 °C. Meanwhile, the UV-vis diffuse reflectance spectra demonstrated that the band-gap of the obtained TNAs was narrower than the commercial TiO2 nanoparticles, indicating a better photocatalytic activity of the as-prepared TNAs over the commercial TiO2 nanoparticles.

On-Demand Hydrogen Generator Based on the Reaction between Aluminum Slurry and Alkaline Solution

In the present work, the aqueous slurry containing 30 wt% solid aluminum particles was prepared, using paraffin oil and oleic acid dispersant and surface active agent respectively. The results showed that no obvious aluminum particle sediment was observed even after being kept it at room temperature in air up to 15 days. The hydrogen generator based on the reaction of the aluminum slurry and sodium hydroxide aqueous solution was manufactured and could supply a maximum hydrogen flow rate of 20 NL/min. The dew point of the hydrogen from the generator was lower than -40oC, indicating the high purity of the as-obtained hydrogen. As expected the X-ray diffraction patterns revealed that the byproduct was bayerite.